1. Field of the Invention
The present invention generally relates to a sheet processing apparatus for processing paper (sheets) discharged from an image forming apparatus, such as a printer and a copier, and, more particularly to a sheet processing apparatus having a mechanism for setting paper (sheets).
2. Description of the Related Art
In recent years, a sheet processing apparatus for receiving recorded paper (sheets) discharged from an image forming apparatus, such as a printer and a copier, and for applying predetermined post-processing to the recorded sheets has become widely used. This is because of the fact that an image forming apparatus, which assures high productivity by being provided with means for stapling, punching (or circularly boring), and folding paper, has come into common use, with promotion of the conversion of the image forming apparatus to an online apparatus and with enhancement of the record productivity of the image forming apparatus.
Among such sheet processing apparatuses, there has been a sheet processing apparatus in which, for example, stapling is performed by a stapling unit after recorded paper sheets are received and stacked on a stapling tray (that is, a compiling tray) and a sheet bundle includes a predetermined number of sheets is produced. Hitherto, there have been techniques of providing a predetermined regulating member on a stapling tray in such a sheet processing apparatus in such a way as to extend in a direction of thickness of a sheet so as to enhance ability to stack sheets on the stapling tray, as disclosed in JP-A-11-130338. Further, there have been techniques, which are applied to such a processing apparatus, for performing outward three-folding processing (that is, z-folding) on recorded paper sheets and for aligning the paper sheets by stacking the z-folded sheets on a stapling tray, that is, a compiling tray as disclosed in JP-B-7-49350.
Meanwhile, Z-folded paper has been subjected to folding, and thus has become pliant. Consequently, there has been a fear that when a new paper sheet (that is, a z-folded sheet) is discharged onto paper sheets that have already been aligned on a compiling tray, this new paper sheet may strongly hit the topmost one of the sheets aligned on the compiling tray and disturb the alignment of the sheets. Incidentally, this technical problem may occur not only in the case that Z-folded sheets are discharged to the compiling tray, but in the case that, for example, pliant cardboards are discharged to the compiling tray.
Incidentally, JP-A-11-130338 discloses techniques for providing a regulating/pressing member adapted to guide rear edges of paper sheets, and for moving this regulating/pressing member in the direction of thickness of a paper bundle according to the number of paper sheets stacked on the stapling tray. This official gazette describes that even when the number of paper sheets changes, rounded paper sheets can favorably be aligned. However, it is difficult to enhance ability to accommodate the paper sheets, which are heated and pressured and extended by, for instance, a fixing portion, simply by moving the regulating/pressing member in the direction of thickness of paper sheets to thereby change the thickness of the paper sheets. To enhance the quality of alignment of paper sheets on a tray, such as a stapling tray, for stacking discharged paper sheets (that is, output paper sheets on each of which an image is formed), it is preferable that an appropriate conveyance force is stably provided to the paper sheets. JP-A-11-130338 does not describe this problem.
Further, paper sheets to be stacked are not limited to plain paper used in design. For example, z-folded paper sheets and extremely thick paper sheets described in, for instance, JP-B-7-49350 may be used as the paper sheets to be stacked. In the case of the techniques disclosed in JP-A-11-130338, the regulating/pressing member is moved according to the number of paper sheets. However, when folded paper sheets or thick paper sheets are supplied, the thickness of a sheet bundle is thicker than a total thickness of sheets of the number, which are to be counted. Thus, the situation of the stacked paper sheets largely changes according to the kind of paper sheet to be stacked. Consequently, even when the regulating/pressing member is moved in the direction of thickness of a sheet bundle, sufficient functions cannot be obtained. Especially, in the case of a z-folded paper sheet, swells frequently occur at folded parts thereof. Failures of alignment are liable to occur.
According to the techniques disclosed in JP-A-11-130338, only the regulating/pressing member is simply moved. For instance, sometimes, drive members adapted to provide a predetermined conveyance force for alignment are caused to perform up-and-down motions. In such a case, when stacked paper sheets are not sufficiently controlled, the conveyance force largely deviates from a design value thereof. Thus, serious damage may be caused to paper sheets.
Further, Z-folded paper described in JP-B-7-49350 has been subjected to folding, and thus has become pliant. Consequently, there has been a fear that when a new paper sheet (that is, a z-folded sheet) is discharged onto paper sheets that have already been aligned on a compiling tray, this new paper sheet strongly hits the topmost one of the sheets aligned on the compiling tray and disturbs the alignment of the sheets. To obtain good ability to align paper sheets that are extremely thick, it is required to provide an appropriate conveyance force onto the thick paper sheets and to perform a putting-aside operation on the paper sheets with favorable conveyance timing.
In recent years, there have been demands for high-speed sheet processing. Thus, when a sheet processing apparatus is connected to an image forming apparatus that outputs paper sheets, on each of which an image is formed, at high speed, it is necessary to significantly reduce time required for alignment of paper sheets. To meet such necessity, it is demanded that high-speed alignment of page sheets is realized, and that even when such high-speed alignment is achieved, various kinds of paper sheets are orderly stacked.